1. Field of the Invention
The present invention relates to a feedback automatic control method and apparatus. More specifically, the present invention relates to a feedback automatic control method and apparatus adapted for making feedback control such that a control amount of an object being controlled may correspond with a target value.
2. Description of the Prior Art
A feedback automatic control apparatus adapted for opening or closing a gate by controlling the same such that the water level of a dam may be a target value in a hydraulic power generating station, for example, has been hitherto employed.
FIG. 1 is a block diagram of a conventional feedback automatic control apparatus. Referring to FIG. 1, the structure of a conventional feedback automatic control apparatus will be described. A control portion 1 is adapted to set in a first comparator 2 a target value of the water level of a dam and is also adapted to set in a second comparator 5 a dead zone having a predetermined width .beta. contiguous to the target value. The width .beta. of the dead zone is set for discontinuing control for opening/closing a gate, not shown, by deeming that the actual water level has reached the target value, if and when the water level of a dam is within such range. The first comparator 2 is supplied with a detected signal from a water level sensor 4 for detecting the actual water level 3 of the dam. The first comparator 2 compares the target value and the actual water level, thereby to evaluate a deviation value to provide the same to the second comparator 5. The second comparator 5 compares the dead zone as set and the deviation obtained from the first comparator 2, so that an operation command signal is applied to a gate driving circuit 6 so that the deviation may be decreased. Accordingly, the gate driving circuit 6 controls the gate of the dam to open/close the same, thereby to change the flow out amount of the water.
FIG. 2 is a graph showing a change of the control amount in the FIG. 1 conventional feedback automatic control apparatus. Now an operation of the conventional feedback automatic control apparatus will be described. The control portion 1 sets in the second comparator 5a dead zone having a predetermined width .beta. shown in FIG. 2 and provides the first comparator 2 with a target value contiguous to the upper limit of the dead zone. The first comparator 2 compares the water level detected by a water level sensor 4 at the start of control and the target value, thereby to evaluate a deviation. The second comparator 5 compares the deviation supplied from the first comparator 2 and the dead zone, thereby to provide the gate driving circuit 6 with an operation command signal associated with the deviation, if and when the detected water level is not within the range of the dead zone. The gate driving circuit 6 is responsive to the operation command signal to open/close the gate, thereby to adjust the water level of the dam. If and when the water level of the dam is within the range of the width .alpha. of the dead zone, an operation command signal is supplied from the second comparator 5 to the gate driving circuit 6, thereby to discontinue control for opening/closing the gate.
Since a conventional feedback automatic control apparatus is adapted such that a dead zone having a predetermined width .beta. at the start of control is set and the gate is opened/closed such that the opening/closing amount of the gate, i.e. the water level by way of the control amount may be a target value without changing the set dead zone, it follows that opening/closing of the gate is frequently made. More specifically, in the case where the width .beta. of the dead zone as set is narrow, the water level by way of the control amount as detected by the water level sensor 4 comes slightly off the target value and each time comes off the dead zone, with the result that the gate is frequently opened or closed. Furthermore, a disadvantage is involved that at the start of control, as shown in FIG. 2, an overshoot of the control amount with respect to the target value is increased. Conversely, by increasing the width .beta. of the dead zone, the frequency of opening/closing the gate is decreased; however, an operation could be in a stable state in the case where the actual water level comes off the target value, in which case a disadvantage is involved that accuracy of the actual water level with respect to the target value is degraded.